Results from Test Project

Fall 2023

Test Project

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Soil Health

Soil health is a term that describes how well a soil ecosystem supports plants, animals, and humans. It also recognizes the living nature of soils and the importance of soil microorganisms. Healthy soils can provide wildlife habitat, support biodiversity, reduce the effects of climate change, filter air and water, increase crop productivity and food security, and ensure thriving rural economies.

Qualities of a Healthy Agricultural Soil
  • Good soil tilth allows roots to penetrate
  • Near neutral pH (6–8) maximizes nutrient availability for most crops, and minimizes Al and Mn toxicity
  • Sufficient—but not excessive—nutrient supply for crop growth
  • Small population of plant pathogens and pests
  • Adequate soil drainage and infiltration
  • Diverse and active microbial population
  • Low weed seed bank
  • No residual chemicals or toxins that may harm the crop, including salts
  • Resistance to degradation such as from erosion or surface runoff

Soil Science 101

A crucial part of the soil health journey is measuring changes in your soil and understanding how to interpret those measurements. We can measure soil health with a range of indicators describing a soil’s physical, chemical, and biological properties, which can relate to important soil functions. Each indicator measures a different property of the soil and can be affected differently by management.

To learn more about management practices that support healthy soil, check out these resources from the Natural Resources Conservation Service (NRCS) principles of building soil health.

What We Measured in Your Soil

Soil Texture is the relative proportion of sand, silt, and clay-sized particles in your soil. Imagine these particles like basketballs, golf balls, and poppy seeds, which are very different in size even though soil particles don’t appear different to the naked eye. Importantly, soil texture describes only the mineral portion of the soil and is not affected by organic matter or management. However, soil texture is a significant driver of how soils respond to management. Soils with higher clay content can hold more nutrients, organic matter, and water than sandy soils. This is because clay particles have high surface area and electrical charge and create small soil pores. Soils with high sand content have larger pores, and cannot hold as much water.

Figure showing size comparisons of soil particles (sand, silt, and clay) to common circular items (basketball, golf ball, and poppy seed)

Comparison between uncompacted and compacted soil. Uncompacted soil particles are more spread out, while compacted soil particles are closed together.

Bulk Density is the mass of particles within a certain volume of soil and is used as an indicator of soil compaction. Bulk density varies depending on soil texture and structure and is greatly affected by tillage, tractor passes, and organic matter inputs. It is a primary determinant of soil aeration, porosity, water infiltration, and root growth. For more information on the special equipment required to measure bulk density, consult this NRCS protocol.

Soil pH describes how acidic (pH less than 7.0) or alkaline (pH greater than 7.0) the soil is, and is a measure of the concentration of hydrogen ions in the soil solution. Many essential nutrients like P, Fe, Mn, Zn, Cu, Co, and B become less plant-available at alkaline pHs. Other nutrients like Al or B can become toxic at acidic pHs. Soil pH also greatly affects what microbial populations can live in the soil. Soil pH is impacted by inherent qualities of the soil such as its age, mineralogy, and rainfall zone. It is also impacted by fertilization, irrigation water pH, and SOM content. Most agricultural crops grow best in neutral soil pHs, within a range of 6 to 8. Soil pH can be lowered using sulfur or raised by adding agricultural lime.

Total Nitrogen is a measurement of both inorganic (plant-available nitrate and ammonium) and organic (typically not plant-available) nitrogen in the soil. Having sufficient total nitrogen in the soil is key for promoting mineralization, or the process of changing the organic nitrogen to a form that plants can use.

Soil Health Indicators

The below table describes: 1. What each indicator helps measure in your soil; 2. Whether you want the measured value to be higher (more is better), lower (less is better), or in the middle (optimal range); and 3. How often to measure each indicator. Our understanding of these indicators is rapidly evolving as researchers measure them in diverse soils, cropping systems, and climates.

More is better scoring curveOptimal range scoring curveLess is better scoring curve

Soil Health Indicator

Soil Function

Scoring Curve Type

Measure every: 1-3 years

ACE Soil Protein

Nutrient cycling, biodiversity & habitat, filtering & resilience

More is better

Aggregate Stability

Physical support, water relations, biodiversity & habitat, filtering & resilience

More is better

Electrical Conductivity (EC)

Physical support, nutrient cycling, filtering & resilience

Less is better

Mineralizable Carbon

Nutrient cycling, biodiversity & habitat, filtering & resilience

More is better

Permanganate Oxidizable Carbon (POXC)

Biodiversity & habitat, nutrient cycling, filtering & resilience

More is better

Potentially Mineralizable Nitrogen (PMN)

Nutrient cycling, biodiversity & habitat, filtering & resilience

More is better

Soil pH

Nutrient cycling, filtering & resilience

Optimal range

Total Nitrogen

Nutrient cycling, biodiversity & habitat, filtering & resilience

Optimal range

Plant Essential Nutrients

Nutrient cycling

Optimal range

Measure every: 3-5 years

Bulk Density

Physical support, water relations, biodiversity & habitat, filtering & resilience

Optimal range

Cation Exchange Capacity

Nutrient cycling, filtering & resilience

More is better

Infiltration

Water relations, physical support

More is better

Soil Organic Matter (SOM)

Nutrient cycling, filtering & resilience

More is better

Water Holding Capacity (WHC)

Water relations, physical support

More is better

Soil Health Testing

Infographic titled How to Get Quality Results. Be Consistent: sample at the same time each year; send samples to the same lab; keep samples cool and get them to the lab quickly; keep good records of lab results. Context matters: not all soils are created equal; indicators are impacted by inherent properties like climate and soil texture; as well as by management; don't be alarmed if your soil is below the optimal range fro some indicators, see how far you can take your soil with management but know there may be inherent limitations. Back to the Basics: old school measurements like pH, texture, and soil organic matter are still incredible important; new indicators are constantly being developed, don't feel you have to measure all of them, or let the process overwhelm you; have fun exploring through a soil health lens, but remember that you know your soil better than anyone! Be Patient: some measurements may not change as quickly as you'd like; sampling across time is very important, our scientific understanding of these measurements is evolving; we are all on this journey together.

Looking Forward

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